Ignition coil for internal combustion engine

ABSTRACT

An ignition coil for an internal combustion engine comprises a spirally wound sheet of silicon steel. The sheet of silicon steel has a series of slits extending in substantially parallel relation transversely thereof and closely adjacent each other, the slits terminating short of the opposite side edges of the sheet. The spirally wound silicon sheet is inserted into a dielectric winding cylinder or form for the primary and secondary windings of the ignition coil, and the wound sheet bulges intermediate its axially opposite ends to closely engage the winding core. The sheet tends to unwind to some extent, and this leaves an axially extending opening at the center of the wound core, this axially extending opening having a diameter not more than one-half the internal diameter of the winding core.

O Unlted States Patent [151 3,680,017 Shiari et a]. 1 July 25, 1972 {54] IGNITION COIL FOR INTERNAL 1,883,905 10/1932 Hartzell ..336/213 x COMBUSTION ENGINE 2,142,066 12/1938 Eppelsheimer ....336/234 X 721,289 2/1903 Depp et al ....336/234 X 21 Inventors: Yeehilhiehi Shim: Teehimi Kemorl. both 1,550,889 8/1925 Donan ....336/213 x of Kanya, Japan 1,647,417 1 1/1927 Schneider. ..336/234 X 1,835,870 12/1931 Henry ..336/234 X [73] Ass'gnee' gr 2" 2,107,973 2/1938 Bajon..... ....336/234 x apa 2,282,040 5/1942 Doran ....33o/234 x [22] Filed: March 23, 1971 3,195,082 7/1965 Wetherill et a1. ..336/21 2 X [21] Appl' 127'173 Primary Examiner-Thomas .I. Kozma thud U S Application Armrney-McGlew & Tuttle [63] Continuation-impart of Ser. No. 33,157, May 5, 1970, [57] ABSTRACT abandoned which is a continuation of Ser. No.

An 1gn1t1on co1l for an 1nternal combust1on englne comprises a May 1968 abandoned spirally wound sheet of silicon steel. The sheet of silicon steel has a series of slits extending in substantially parallel relation [30] Ford! Application My Data transversely thereof and closely adjacent each other, the slits May 15, 1967 Japan ..42/30773 terminating short of the pp side edges of the sheet- The spirally wound silicon sheet is inserted into a dielectric wind 52 us. c1. ..336/213, 336/233 s cylinder er form for the P y and secondary Wihdinzs 51 Int. Cl. ..H0lt27/24 of the ignition coil, and the l! intermediate 53 Field at Search ..336/233 234 213 210, 212 axially P ends engage the Winding The sheet tends to unwind to some extent, and this leaves an 56] Rdmnces Cited axially extending opening at the center of the wound core, this axially extending opening having a diameter not more than UNITED STATES PATENTS one-half the internal diameter of the winding core. 2,962,679 1 1/1960 Stratton ..336/234 X 5 Claims, 6 Drawing Figures CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 33,157, filed May 5, 1970, for PARAMAGNETIC CORE FOR IGNITION COILS OF IN- TERNAL COMBUSTION ENGINES" and which is a streamline continuation of application Ser. No. 726,712, filed May 6, 1968, for PARAMAGNETIC CORE FOR IGNITION COILS OF INTERNAL COMBUSTION ENGINES", both of which are now abandoned.

BACKGROUND OF THE INVENTION The iron cores of convention ignition coils, for internal combustion engines, have generally required a preselected number of rectangular sheets of silicon steel which are laminated to form a rectangular cross section prism. This iron core or prism is inserted into the center of the ignition coil windings, such as the secondary winding 2 and primary winding 3, shown in FIGS. I and 2, and previously wound on a cylindrical dielectric core or form 1, such as a winding form of paper.

In such conventional constructions, considerable time is required to laminate the necessary number of rectangular silicon steel sheets, and to insert the resulting rectangular cross section laminated core into the center of the windings 2 and 3 as an iron core 4. In particular, it is very difficult to effect these operations automatically.

Furthermore, from the standpoint of performance, there is a disadvantage in that, since the iron core 4, formed of rectangular silicon steel sheets, is inserted in a cylindrical winding form 1, a space 7 results between the core 4 and the inner surface of the cylindrical winding form. This results in the voltage generated in secondary winding coil 2 by a magnetic coupling with primary winding coil 3 being relatively low.

SUMMARY OF THE INVENTION This invention relates to ignition coils for internal combustion engines and, more particularly, to an improved iron core for such ignition coils resulting in much more efficient operation thereof as well as decreasing the expense and lessening the weight thereof.

In accordance with the present invention, a relatively elongated and substantially rectangular silicon steel sheet is formed with a series of closely adjacent parallel slits extending transversely thereof but terminating short of both longer edges of the sheet. The slit sheet is then wound into a spiral and the wound sheet is inserted within the winding form for the primary and secondary coils or windings of the ignition coil. When the wound sheet is inserted into the winding core, which may be a paper cylinder, for example, the sheet tends to unwind somewhat and the outer convolutions are in firm engagement with the winding form and thus in close relation with the secondary winding of the ignition coil. The tendency of the spiral silicon sheet to thus unwind, results in there being an axial passage through the core of the ignition coil. Thus, the mass of the core is concentrated at the winding form, and thus is closely adjacent the secondary winding of the ignition coil.

A further feature is that the slit portion of the wound core bulges outwardly, as compared to the continuous edges of the wound sheet, thus further concentrating the iron of the core at the winding form and thus at the secondary winding of the ignition coil.

An object of the invention is to provide an improved core for an ignition coil such as used with internal combustion engines.

Another object of the invention is to provide such a core in which there is a reduction in the iron loss due to eddy currents as well as a reduction in the loss of magnetic flux.

A further object of the invention is to provide such a core in which the mass of the core is concentrated immediately adjacent the secondary winding of the ignition coil, thus greatly improving the magnetic coupling between the primary and secondary windings of the ignition coil.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. I is a longitudinal or axial sectional view through a conventional ignition coil for internal combustion engines;

FIG. 2 is a top plan view of the coil shown in FIG. 1;

FIG. 3 is a longitudinal or axial sectional view through an ignition coil having an iron core formed in accordance with the present invention;

FIG. 4 is a top plan view of the ignition coil shown in FIG. 3;

FIG. 5 is a developed view of the iron core embodying the present invention; and

FIG. 6 is an elevation view of the iron core.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the present invention, a relatively elongated substantially rectangular silicon steel sheet is formed with transversely extending and substantially parallel slits which are spaced as near each other as possible. These slits temiinate short of the opposite longitudinal edges of the sheet. The sheet is then spirally wound to form an iron core 4, as shown in FIGS. 3 and 4, for example, for an ignition coil. The sheet is indicated in developed form at 8 in FIG. 5 as formed with the closely spaced slits 6. The wound silicon steel core 4 has a much better performance, with respect to iron losses due to eddy currents and with respect to magnetic flux losses, than does the iron core 4 shown in FIGS. 1 and 2. The reason for this is that the space between the core and the cylindrical winding form 1 is greatly decreased so that, with the total amount of iron or silicon steel less than that of a conventional iron core formed of rectangular silicon steel sheets stacked on each other, the performance of the ignition coil having a core in accordance with the invention is equal to or better than that of a conventional ignition coil.

Furthermore, with respect to manufacture of the core, since the unwinding force becomes small due to the resilience of the silicon steel sheet, no particular measures to prevent unwinding of the spirally wound silicon steel sheet are especially required. The winding of the core is made especially easy and there is a close fit within the cylindrical dielectric winding form due to a bulge 9 of the iron core formed by the slit portion of the silicon steel sheet. Consequently, the assembly of cores into the winding forms of ignition coils is made very simple as compared with a conventional iron core comprising stacked rectangular silicon steel sheets which form a rectangular cross-section prism. Thus, the iron core for an ignition coil embodying the invention can be readily assembled automatically.

Referring more particularly to FIG. 5, which illustrates a developed view of the silicon steel sheet 8 having a width a and a length I, this sheet is formed with closely adjacent substantially parallel slits extending transversely thereof but terminating short of the two opposite longitudinal edges of sheet 8. Thus, the slits 6 are formed in sheet 8 at as small a spacing as possible.

In FIG. 4, the iron core 4 has been formed by spirally winding silicon steel sheet 8 having the slits 6, and the core 4 is inserted into a cylindrical dielectric, such as paper, winding form 1 on which there are wound a secondary coil 2 and a primary coil 5. As will be clear from FIGS. 3 and 4, there is cylindrical space extending axially of the spiral iron core 5. a

The closely spaced slits 6 facilitate winding of the silicon steel sheet 8, thereby facilitating reduction in the diameter of the iron core 4. After winding, the unwinding force of the cylindrical silicon steel sheet is decreased due to the spring effect. Thus, preventative measures against unwinding, such as spot welding, are not necessary.

There are several advantages to forming the silicon steel sheet 8 with the closely spaced slits 6 which terminate short of the longer edges of the sheet. Among these is the decrease in the iron loss by eddy currents, as compared with an iron core comprising stacked rectangular steel sheets forming a rectangular cross-section prism. Naturally, the reduction in the iron loss due to eddy currents improves the performance of the ignition coil.

Additionally, the slits 6 not only facilitate winding of sheet 8 into a spiral core but also the wound sheet closely contacts the inner surface of the cylindrical dielectric or paper winding form 1, due to the bulge 9 of iron core 4' as shown in FIG. 6 and which occurs after the winding. This is very advantageous as compared with a conventional ignition coil in which there is a magnetic flux loss due to the relatively large space 7, as shown in FIGS. 1 and 2, formed between the rectangular cross-section iron core 4 and the inner wall of the cylindrical winding fonn 1. This space 7 lowers the generated voltage.

Particularly in the case of ignition coils for automobiles, the distance between the primary coil 3, which is an exciting source, and the iron core 4, is relatively large. Consequently, the strength of the magnetic field due to the magnetomotive force of primary coil 3 varies greatly within primary coil 3 in accordance with the radial direction. For this reason, in an ignition coil for automobiles, in proportion to the proximity to the primary coil 3 or, in other words, in proportion to the proximity to the inner surface of the winding form 1, the strength of the magnetic field increases and, at the center of axis of cylindrical form 1, the strength of the magnetic field decreases.

Accordingly, when an iron core 4 embodying the invention is inserted into the cylindrical winding form 1, an open space 5 having a diameter of about one-half the internal diameter of core 1 is formed in the center of the wound silicon steel sheet 8. The space 7 between a conventional iron core, comprising stacked rectangular silicon steel sheets forming a rectangular prism, and the inner surface of a cylindrical winding form, is entirely eliminated. Consequently, the silicon steel sheet 8 can be strongly magnetized and, on that account, the effective amount of magnetic flux produced by steel sheet 8 is greatly increased so that the voltage developed in secondary coil 2 can be very substantially increased. This enables a substantial reduction in the amount of silicon steel sheet necessary to generate, in secondary coil 2, a voltage equal to that generated in a conventional ignition coil such as shown in FIGS. 1 and 2.

The reason why the diameter of the cylindrical space 5 has been selected to be about one-half the inside diameter of the cylindrical winding form 1 will now be pointed out. ln the first place, the outside diameter of a winding arbor on which the silicon steel sheet 8, formed with the slits 6, is wound forms a space, and experiments have indicated that the outside diameter of the winding arbor should be at least 6 mm.

In the second place, the silicon steel sheet 8 with the closely spaced slits 6 terminating short of the opposite longer edges thereof is spirally wound and then the wound silicon steel sheet is inserted into the cylindrical dielectric or paper winding form 1. The insertion is made in such a manner that there is no space 7 between the inner surface of winding form 1 and the exterior surface of iron core 4, and it will be noted that such a space 7 is a substantially disadvantage in the case of a conventional iron core 4 formed of stacked rectangular silicon steel sheets forming a rectangular cross-section prism. As a result, the silicon steel sheet core 4 of the present invention can be magnetized very strongly. Thus, that portion of the silicon steel sheet corresponding to the central part of a conventional iron core 4, as shown in FIGS. 1 and 2, is not necessary, so that the cylindrical space 5 serves the purpose up to a certain size. However, when cylindrical space 5 is increased in size or diameter too much, performance is lowered due to the reduction in the amount of iron.

Experiments with respect to this relationship, involving a primary winding having 300 turns and a secondary winding having 20,000 turns with the inside diameter of the winding form being 16 mm, indicate that the generated voltage does not vary when the diameter of the open cylindrical space 5 is two-fourth or less than the inside diameter of the winding form, and that the generated voltage is decreased, due to lack of sufficient iron, when the diameter of the open cylindrical space 5 is two-fourth or more of the internal diameter of the winding form i. It has been confirmed by experiment that these considerations can be applied to an ignition coil for automobiles in practical use at the present time, in addition to the particular example selected for the experiment.

An example of an experiment with the iron core for an ignition coil in accordance with the present invention will now be set forth. For comparison with a conventional iron core comprising rectangular silicon steel sheets stacked to form a rectangular cross-section prism, an iron core embodying the present invention and an iron core in accordance with conventional practice were inserted in the same ignition coils, and the voltage generated in the secondary coil at the time of interrupting a current of l A was measured. The interval between the slits 6 of the iron core embodying the invention was 3 mm. The results of the measurements are indicated in the following table:

As will be clear from the above table, the experiment shows that the use of an iron core 4', embodying the present invention, enables a reduction in the weight of the iron core by 37 percent as compared with a conventional iron core such as shown in FIGS. 1 and 2. The performance, as represented by the voltage generated in the secondary coil at the time of interrupting a current of l A, is equal to or greater than that of the conventional iron core 4. These good results are obtained only with an iron core 4', formed by spirally and tightly winding a silicon steel sheet 8 formed with closely adjacent slits 6, in such a manner that the cylindrical open space 5 has a diameter which is about half the inside diameter of winding form 1, with the wound silicon steel sheet being inserted into the winding form 1.

As mentioned above, in the iron core 4' embodying the invention, the closely spaced slits 6 terminate short of both opposite longitudinal edges of sheet 8, so that these edges are continuous throughout the length of sheet 8. The sheet 8, with the slit 6, is spirally wound in such a manner that the resulting open cylindrical space 5 has a diameter of about one-half the inside diameter of the cylindrical winding form 1. After winding, the wound silicon steel sheet 8 is inserted in close contact with the inner surface of winding form 1, and such close contact is facilitated by the development of a bulge 9 as a result of the closely spaced slits 6. Thus, a magnetic flux can be most effectively produced in iron core 4', as compared to the conventional ignition coil having a space 7 between the inner surface of form 1 and the iron core 4, as shown in FIGS. 1 and 2. There is thus obtained the advantageous effect that the voltage generated in the secondary coil can be very substantially increased, and this, in turn, means that the quantity of expensive silicon steel sheet used in the core can be greatly reduced to produce a secondary voltage which is at least equal to that produced in a conventional ignition coil. Thus, there is a very substantial reduction in the cost of an ignition coil having an iron core 4' in accordance with the present invention.

Since an open cylindrical space 5, having a diameter which is about half the inside diameter of cylindrical winding form 1, is formed at the center of iron core 4, a high speed, continuous and automatic manufacturing of the iron core is greatly facilitated. in addition, since an iron core 4 embodying the invention has a bulge 9 developed due to the closely spaced slits 6, when the portion of iron core 4', as shown in FIG. 6, is inserted within winding form 1 as a guide, that portion also comes into close contact with the inner surface of winding form 1 due to the force trying to expand bulge 9 and even without using a special method of asembly. Thus, as compared with a conventional iron core 4 such as shown in FIGS. 1 and 2, automatic insertion of an iron core 4' embodying the invention is made possible, resulting in a substantial reduction in the manpower required for assembling the cores.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. An ignition coil, comprising a tubular winding form, secondary coils wound on said winding fonn, primary coils wound on said secondary coils, and an iron core inserted into said winding form coaxially thereof, said iron core comprising a spirally wound, relatively elongated and substantially rectangular sheet of silicon steel having a radially outwardly projecting bulge therein intermediate the axially opposite ends thereof and engaged with the inner peripheral surface of said winding form.

2. An ignition coil, as claimed in claim 1, in which said sheet of silicon steel has closely adjacent, substantially parallel slits extending thereacross and terminating short of both longer edges of said sheet.

3. An ignition coil, as claimed in claim I, in which said core has an axially extending, substantially cylindrical open space therethrough at its center.

4. An ignition coil, as claimed in claim 1, in which the outer diameter of the axially opposite ends of said core is substantially equal to the inner diameter of said winding fonn.

5. An ignition coil, as claimed in claim 3, in which the diameter of the open space of said core is of the order of onehalf the inner diameter of said winding form.

i I! i i Q Patent No.

Dated July 25, 1972 Inventor(s) Yoshimichi Shirai et a1.

Yoshimichi Shirai (SEAL) Attest:

Attesting Officer EDWARD M.PLETCHER,JR.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet [72] "Yoshimichi Shiari" should read Signed and sealed this 21st day of November 1972.

ROBERT GOTTSCHALK Commissioner of Patents FORM PO-1050 (10-69) USCOMM-DC 6O376-P69 U.S. GOVERNMENT PRINTING OFFICE 3 I969 O366-334v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,680,017 Dated July 25, 1972 Yoshimichi Shirai et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet [72] "Yoshimichi Shiari" should read Yoshimichi Shirai Signed and' sealed this 21st day of November 1972.

(SEAL) Attest: I

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PC4050 USCOMM-DC wan-ps9 9 U.S. GOVERNMENT PRINTING OFFI CE: I969 0-366-334.

Patent No. 3,680,017 Dated July 25, 1972 Yoshimichi Shirai et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet [72] "Yoshimichi Shiari" should read Yoshimichi Shirai Signed and'sealed this 21st day of November 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 60376-P59 U S. GOVERNMENT PRINTING OFFICE 1 I969 O366-334.

F ORM PO-105O (10-69) 

1. An ignition coil, comprising a tubular winding form, secondary coils wound on said winding form, primary coils wound on said secondary coils, and an iron core inserted into said winding form coaxially thereof, said iron core comprising a spirally wound, relatively elongated and substantially rectangular sheet of silicon steel having a radially outwardly projecting bulge therein intermediate the axially opposite ends thereof and engaged with the inner peripheral surface of said winding form.
 2. An ignition coil, as claimed in claim 1, in which said sheet of silicon steel has closely adjacent, substantially parallel slits extending thereacross and terminating short of both longer edges of said sheet.
 3. An ignition coil, as claimed in claim 1, in which said core has an axially extending, substantially cylindrical open space therethrough at its center.
 4. An ignition coil, as claimed in claim 1, iN which the outer diameter of the axially opposite ends of said core is substantially equal to the inner diameter of said winding form.
 5. An ignition coil, as claimed in claim 3, in which the diameter of the open space of said core is of the order of one-half the inner diameter of said winding form. 